Carbon nanotubes can be classified by the number of walls in the tube, single-wall, double wall and multiwall. Each wall of a carbon nanotube can be further classified into chiral or non-chiral forms. Carbon nanotubes are currently manufactured as agglomerated nanotube balls or bundles.
It is desirable to use carbon nanotubes (also known as carbon nanotube fibres) as a reinforcing agent in elastomer composites. However, utilization of carbon nanotubes in these applications has been hampered by the general inability to reliably produce discrete or individualized carbon nanotubes. To reach the full potential of performance enhancement of carbon nanotubes as composites in elastomers the carbon nanotubes need to be separated. In this context one may also speak of exfoliated, debundled, disentangled or discrete nanotubes. All of these terms intended to describe individual nanotubes, i.e. nanotubes that are separated from other nanotubes.
Various methods have been developed to debundle or disentangle carbon nanotubes in solution. For example, carbon nanotubes may be shortened extensively by aggressive oxidative means and then dispersed as individual nanotubes in dilute solution. These tubes, however, are too short for use as reinforcing materials, especially in high strength composite materials.
Useful procedures to produce discrete nanotubes are disclosed in US 2011/0151321, WO 2010/117392 and Wang et al., Carbon 41 (2003) 2939. The entire disclosure of these references is hereby incorporated by reference.